Imagine you have a toy that you really love playing with, but someone takes that toy away and won't let you play with it anymore. That would be really mean and make you feel sad, right?
Well, sometimes, grown-ups can be really mean to other grown-ups or even to kids, and it's called abuse. Abuse can happen in different ways, but it basically means someone is hurting another person on purpose, and that's not okay.
For example, if someone hits you or makes you feel scared all the time, that's abuse. Or if someone touches you in a way that makes you uncomfortable, that's abuse too.
When someone experiences abuse, it's important for them to tell a trusted adult, like a parent or teacher, because nobody deserves to be treated in a hurtful way. There are people who can help and get the person out of the situation, so they can feel safe and happy again.